Resonator ukuleles have the volume of banjo ukes, but with more sustain.
The East-Asian ones (brass, most often with a nickel plating) are generally not worth much. Loud: yes, playable: yes; very good: no. Recording King, Kala, Johnson, Regal, Gretsch, Luna, Ashbury, Kala fall into this category.
It's true that it's a high step up pricewise from there. From there it's a leap up to the 1000-and-above category. Stuart Wailing makes one-offs as well for a mid-way price, but they're quite heavy and not to everyone's liking.
In the upper bracket, there are antique ones, NRP ones (steel, wood, brass), Fine Resophonic ones (in a modernistic style, or the very rare inverted spider cone ones) and a host of bespoke luthiers: Argapa, DonMo, Beltona, Mya-Moe and Argapa have been mentioned, Ron Philips makes the Del Rey ones but they're very rare. Paul Beard makes wood-bodies ones. Pete Howlett makes very good ones as well, in an art deco style.
'Steel ukulele' is not a very good term. I thought at first it might be about playing lap style (with a steel bar, as in 'steel guitar') or having steel strings on a ukulele. Resonator describes the instruments better, regardless of the body material (either brass, german silver, steel or wood) and the cone system (forward facing 'spider' cones, backward facing 'biscuit' cones or the handful of 'tricone' instruments with a backward facing trio of small cones).
As with banjo ukes, resonators require some attention to set-up: if you restring them with care, the intonation can become far off, buzzes and rattles develop and the cone might collapse - even on very high quality instruments. The main tricks are that the bridge is loose and can be twisted (even with the push of a pencil end), tension of the strings should be perpendicular/downward, and the cone can't handle uneven pressure (so restring string by string, or outside strings followed by inside strings).
But they are great instruments, with unrivalled dynamics (soft to loud).